There is another thing that might seem silly, but that gave us a headache.
It is a topic that keeps evolving, therefore what we write could be obsolete in a few weeks.
Anyhow, to make it short: we decided not to go for all the solutions based on temporary sim-cards and similar. The best thing would have been to activate a Vodafone travel sim (http://www.vodafone.co.nz/travel-sim/), at the moment it is possible to do it on a few countries, but the list seems to be constantly increasing.
We simply got a Vodafone data card as soon as we landed, we put it in a smartphone and that’s it. We called with VOIP, used data connection for the phone and therefore we also used the phone as map, everything for about 20 NZ dollars/month with 10 GB of credit in it, it was enough and we had some leftover. But if you are busy at work and you will receive many phone calls even in New Zealand, maybe the bill could be expensive.
Last thing: even if you have a good data card, keep in mind that on the southern island the connection is really bad . We suggest you getting on your smartphone a sat nav that can work offline, otherwise you could have troubles finding your route.